IMac G3 333 Freezes at Seemingly Random Times

Question

Hello all,
I have an iMac G3 333 that runs OS 10.4.10 beautifully... except it locks up/freezes and I can't figure out why. I will use it for a while and then suddenly the mouse pointer stops moving and the keyboard doesn't work. If iTunes is playing the music skips then stops. Nothing happens on the screen. At that point the Mac must be unplugged because the power button doesn't work either. I typically get about 20 minutes of use out of it before a crash. Everything else is normal. If it sits left alone and the screen saver turns on it's happy to sit indefinitely. It also is comfortable waking up after falling asleep.
It is a 333 that I upgraded to 256 MB of RAM (filled both slots). Original 6 gig or so hard drive (I know, cramped, but it works). I also changed the motherboard battery. No other software installed.
Weird part is that this problem also happened when running OS 9.2.2 with the original 32 MB of RAM. At the time, I attributed it to OS 9 extensions. I did do all firmware updates before upgrading to OS 10. I did a complete reformat and reinstall.
I have tried:
memtest in single user mode (all RAM checks out ok)
repair permissions
verify disk (several times and in single user mode)
reset PRAM multiple times
holding the motherboard reset button
reinstalling OS 10.4
not using my surge protector (stupid, but i tried it)
taking the fan out, cleaning all the dust from it, and reinstalling (maybe it was/is overheating?)
I cannot figure out what could be going on. I have spent a lot of time inside Macs (I also tinker with an SE/30), but this one baffles me. If you have a suggestion I would really appreciate it.
Dave

Answer 1

A hard drive that's almost filled to capacity can have problems, especially if there's a lot of fragmentation. The drive could also have a hardware problem that's causing the read/write heads to stick, causing a system hang. If you want to continue using this Mac, I'd install a larger hard drive (120 GBs is the max. retail size that's recognized at full capacity). A worst case scenario would be a flaky processor. I had a G3-333 MHz ZIF processor in a beige G3 that would act up and cause system hangs. Once I replaced it, the quirky behavior disappeared. Unfortunately, your iMac's processor is soldered to the processor card. Unless you really want to keep using it, you should decide if it's worth investing any money trying to troubleshoot the problem.